i used a PR buggy shell. there will be a gap at the back as the truck chassis is longer than the buggy. but i didnt find anything better.
you'll only need it if its wet though.
also, i expect that the rtr will have plastic idler gears in the gearbox, and they may not be able to handle a 7.5t motor for very long.
you'll need two of these.
https://www.insidelinemodels.com/ins...ler-gear-28t-p